At present, large-size display devices such as liquid crystal displays (LCDs) are popularized and become more and more welcome among the public. However, the existing large-size display devices are often unsatisfactory in terms of the quality of the displayed image in which even serious flaws may exist. An important factor with respect to the quality of the displayed image is the length of data lines in the display device. The length of the data lines increases with the size of the display device. Longer data lines have larger impedance, resulting in a large voltage drop over the data lines. This causes the charging voltage of some of the pixels in the display device to be lower than the design value. For example, for the same data line, the data signal supplied by a section of the data line far from the data driver may have a great deviation from the original data signal output from the data driver as compared to the data signal supplied by a section of the data line close to the data driver. Therefore, the pixel electrodes of some of the pixels cannot be sufficiently charged, leading to deterioration of the quality of the displayed image.